How to identify assembled top case after MBP repair?

Solution 1:

The iconography on the 2018 keyboard does differ from that on the 2017 and 2016 keyboards. This can be used to identify the generation.

The YouTube video New 2018 MacBook Pro Keyboards MIGHT fix Keyboard Problems shows the differences between these three models' keyboards. The 2018 option key has a far taller icon than the 2017 option key.

The MacBook Pro 2016 and 2017 models will not receive the 3rd generation MacBook Pro 2018 keyboard according to the MacRumors article: Apple Says Third-Generation Keyboards Exclusive to 2018 MacBook Pro.

Solution 2:

The external keyboard design for the 2018 MacBook Pros is mostly unchanged from its predecessors (except for minor iconographic changes on Option key). There is no way you can visually distinguish between the two.

Under the keyboard replacement program, the eligible MacBooks will receive the same keyboard design as they already have, not the new version (with membrane).

The membrane which is present only in the 2018 MacBook Pros, is installed beneath the keys, and isn't externally visible. This is how the membrane can be seen in the 2018 models:

Image Source: MacBook Pro 13" Touch Bar 2018 Teardown.